Sunscreens compositions are chemical compositions, which are usually applied topically to skin and hair in order to protect them from the damaging effects of the sun's radiation, especially against ultraviolet (UV) radiation.
The damaging effects of sunlight exposure on skin and hair are well documented. These effects include increased incidence of skin carcinogenesis, pigmentation, anomalies and precancerous lesions such as actinic keratosis, melanoma and nonmelanoma skin cancers, as well as accelerated skin aging and undesirable changes in hair quality. In recent years, a growing number of studies show that damage is caused not only by the UVB irradiation (290-320 nm), but also by UVA irradiation (320-400 nm).
The use of UV absorbing chemicals for human application is regulated by the health authorities. In the US and Australia sunscreens are regulated as over-the-counter (OTC) drugs, consequently introduction of new sunscreen active ingredients requires heavy investment of time and money. Most of the UV absorbing agents allowed for use are UVB absorbers. These include para amino benzoates, salicylates, cinnamates, anthranilate, camphors and miscellaneous chemicals. The number of UVA absorbers is more limited, with benzophenones (UVB and UVA absorber) and dibenzoylmethanes (UVA absorber) being the most widely used.
Some of the sunscreen active ingredients have been found to cause photoallergy and photosensitization reactions, encouraging the manufacturers to avoid using them. For example, growing public awareness to the photosensitization reactions of PABA and its derivatives has encouraged the use of PABA free products (see S. Schauder and H. Ippen, European UV Sunfilters, Conference Proceedings, Paris 17-18 November 1998, p. 14). The production of another sunscreen, 4-isopropyl dibenzoyl methane was ceased in 1993 due to the high number of photoallergy incidents reported for this active ingredient (Ibid). Moreover, some of the reported cases of adverse reactions to sunscreen active ingredients relate the adverse reactions to cross reactivity of several sunscreen ingredients, as in the case of cross sensitization between different cinnamate derivatives (Ibid). Moreover, several research groups have demonstrated the photoinduced DNA damage and phototoxicity of several sunscreen agents, including Padimate-O (Knowland et al, FEBS Letters, 324, 309-313, 1993), Phenylbenzimidazole sulfonic acid (C. Stevenson and R. J. H. Davies, Chem. Res. Toxicol, 12, 38-45, 1999). Physical sunscreens such as titanium dioxide are known to be photocatalysts capable of ruptring covalent bonds (U Stafford, K. A. Gray and P. V. Kamat, Heterogeneous Chem Rev. 3, 77-104, 1996), and have been shown to produce reactive oxygen species under illumination (W. C. Dunlap et al, Int. J. Cosmetic. Sci. 20, 1-18, 1998).
With the growing demand for higher SPF values and for broad-spectrum protection, manufacturers are forced to combine several active ingredients at increased concentrations (often the maximum permitted concentrations), hence the problem of cross reactivity between sunscreen active ingredients is becoming more severe. An example for cross reactivity effects is the photoinduced interaction between butyl methoxydibenzoylmethane (also known as 4,4'-methoxy-t-butyldibenzoylmethane or BMDBM), an excellent UVA absorber, with the most widely used UVB absorber octyl methoxycinnamate (R. M. Sayre et. al, 26.sup.th Annual Meeting if the American Society for Photobiology, Abstr. No. SPM-A7). This cross reactivity contributes significantly to the photochemical instability of both the UVB and the UVA active ingredients. Another problem associated with BMDMB that presents a number of composition formulation problem, is its tendency to react with active methylene groups such as those present in formaldehyde releasing preservatives at temperatures above 30.degree. C., thus restricting the use of such preservatives (W. Johncock, Sun Protection The Influencing Factors in Creating Effective Products, March 1999 London, March 1999 and references therein).
Another problem, associated with the use of high sunscreen compounds concentrations, is the tendency of some of these ingredients to crystallize at certain pH range, or if the amount of oil in the composition is not sufficient.
Yet, another problematic aspect in sunscreen products is the selection of packaging material. Liquid UVB filters permeate into various plastic packaging materials (polystyrene as one example), and consequently cause decomposition or coloration of the packaging materials. UV absorbing liquids are able to permeate polymers like polystyrene, low density polyethylene and polyethylene terphthalate. This can cause fracturing of the packaging material, unacceptable colouring of white packaging material with time, and assay problems such as ensuring that the proper content of active ingredients are in maintained upon storage.
In the present invention it has been found that if the sunscreen active ingredients are introduced into the cosmetic vehicle in the form of sol-gel encapsulated sunscreen, cross reactivity of sunscreen active ingredients, e.g. butyl methoxydibenzoylmethane and octyl methoxycinnamate, can be reduced or even prevented. The separate encapsulation of sunscreen active ingredients in the sol-gel derived capsules creates a barrier that prevents cross interactions between these active ingredients. Furthermore, the encapsulation of UV absorbing liquids in sol-gel derived capsules reduces the contact between these liquids and the packaging material. Consequently, the problem of adverse reactions caused following permeation of the sunscreen active ingredients into the packaging material is diminished. Furthermore, the use of sol-gel encapsulated sunscreens facilitate the incorporation, in the same composition, of several components that are incompatible when simply dissolved in the composition, for example 2-phenyl benzimidizole-5-sulfonic acid with .alpha. or .beta. hydroxy acids. The present invention also allows easy incorporation of solid sunscreen active ingredient or active ingredients that tend to precipitate in various compositions, since even in a situation that solid is formed, the crystals are confined within the sol-gel capsules, hence, a pleasant non gritty feel and efficient spreading are maintained. Yet another advantage of the present invention is the ability to control the hydrophilicity/hydrophobicity character by choosing a suitable sol-gel encapsulating material, thus the encapsulated sunscreen can be conveniently introduced into the composition.
It is an object of the present invention to provide safer sunscreen compositions by reducing or even preventing the contact of the light absorbing molecules (sunscreen compounds), or their possible light-induced degradation products, with human tissue.
It is another object of this invention to provide a stable and safer sunscreen composition by reducing or even preventing cross reactivity between various ingredients present in the same composition.
It is a further object of this invention to reduce or even to prevent the deleterious permeation of sunscreen active ingredient into plastic packaging materials which may result in fracturing of the packaging material, unacceptable colouring of white packaging material with time, and assay problems.
It is a further object of this invention to provide the formulator with an easy-to-use sunscreen active ingredients, which can be incorporated easily, without applying heat or high shear forces, in any cosmetically accepted vehicle.
Yet it is another object of the present invention to provide an easy incorporation of solid sunscreen active ingredient or of active ingredients that tend to precipitate, in various compositions, to thereby maintain a pleasant non gritty feel and efficient spreading.
The compositions revealed by this invention are of general nature, and the method according to which they are prepared is applicable to any sunscreen compounds currently used, as well as to sunscreen compounds that will be introduced in the future. It is also applicable for other compounds that are regularly used in cosmetic compositions. Furthermore, because of the easy incorporation of the sunscreen active ingredients and the ability to control their hydrophilicity/hydrophobicity character and the capsules size, the cosmetic vehicle to be used with the sunscreen active ingredients is not limited to any group and can be any cosmetically acceptable vehicle.
In the context of the present invention the term "sunscreen compound" refers to an ultraviolet (UVA and/or UVB) absorbing chemical that can be used in sunscreen composition.
In the context of the present invention the term "sol-gel microcapsule" relates to a core material which is coated by a sol-gel coating matrix.
In the context of the present invention the term "sunscreen active ingredient" refers to sol-gel microcapsules wherein the core material is a sunscreen compound.